Lithium soap grease containing monolithium borate

ABSTRACT

A GREASE COMPOSITION THAT COMBINES GOOD WATER RESISTANCE, GOOD MECHANICAL STABILITY AND HIGH OIL RETENTION WITH EXCELLENT OXIDATION STABILITY AND HIGH DROPPING POINT IS PREPARED BY THE USE OF A NOVEL THICKENER SYSTEM WHOSE ESSENTIAL COMPONENTS INCLUDE A COMBINATION OF THE MONOLITHIUM SALT OF BORIC ACID; AND A LITHIUM SOAP OF A 9-, 10-, OR 12-HYDROXY C12 TO C24 FATTY ACID, E.G., LITHIUM 12HYDROXYSTEARATE. FURTHER IMPROVEMENT IN THIS TYPE OF GREASE RESULTS WHEN A THIRD THICKENER COMPONENT IS INCLUDED, THIS BEING A LITHIUM SALT FORMED IN SITU IN THE GREASE FROM A SECOND HYDROXY CARBOXYLIC ACID OF FROM 3 TO 14 CARBON ATOMS WHEREIN THE OH GROUP IS ATTACHED TO A CARBON ATOM NOT MORE THAN 6 CARBON ATOMS REMOVED FROM THE CARBOXYL GROUP, AND WHEREIN EITHER OF THOSE GROUPS MAY BE ATTACHED TO EITHER ALIPHATIC OR AROMATIC PORTIONS OF A MOLECULE.

United States Patent 01 nee 3,758,407 Patented Sept. 11, 1973 3,758,407LITHIUM SOAP GREASE CONTAINING MONOLITHIUM BORATE Gary L. Harting,Westfield, N.J., assiguor to Esso Research and Engineering Company NoDrawing. Filed Nov. 22, 1971, Ser. No. 201,140

Int. Cl. C10m 5/14 U.S. Cl. 252-18 6 Claims ABSTRACT OF THE DISCLOSURE Agrease composition that combines good water resistance, good mechanicalstability and high oil retention with excellent oxidation stability andhigh dropping point is prepared by the use of a novel thickener systemwhose essential components include a combination of the monolithium saltof boric acid; and a lithium soap of a 9-, 10-, or 12-hydroxy C to Cfatty acid, e.g., lithium 12- hydroxystearate. Further improvement inthis type of grease results when a third thickener component isincluded, this being a lithium salt formed in situ in the grease from asecond hydroxy carboxylic acid of from 3 to 14 carbon atoms wherein theOH group is attached to a carbon atom not more than 6 carbon atomsremoved from the carboxyl group, and wherein either of those groups maybe attached to either aliphatic or aromatic portions of a molecule.

BACKGROUND OF THE INVENTION This invention concerns a modified lithiumsoap grease of premium quality with outstanding properties which includea high dropping point, excellent oxidation stability, long lubricationlife and water resistance.

Lithium greases have been known and widely used for many years. Thelithium soaps that are used as thickening agents for these greases areordinarily prepared by reaction of lithium hydroxide or other suitablelithium base with a conventional high molecular weight acid or acids.The principal advantages of lithium greases have been high waterresistance and ease of dispersion of the soaps in all types oflubricating oil base stocks. Particularly useful have been greasesprepared from lithium hydroxystearate, since the soaps of thehydroxystearic acids and related hydroxy fatty acids have been found tobe more mechanically stable than the corresponding soaps of theconventional fatty acids.

There are many fields of application of grease compositions where a highdropping point is required, as, for example, in the lubrication oftraction motor bearings. The bearings of these locomotives may berequired to operate for periods of as much as three years without anymaintenance, and temperatures as high as 250 F. can be reached in suchbearings.

DESCRIPTION OF THE INVENTION In accordance with the present invention, alithium base grease having excellent oxidation and mechanical stabilityand desirably high dropping points is prepared from a 9-hydroxy,10-hydroxy, or 12-hydroxy C to C preferably C to C fatty acid, and boricacid. Additionally, for further improvement in dropping point, there mayadvantageously be used a second hydroxycarboxylic acid of from 3 to 14carbon atoms, wherein the hydroxy group is attached to a carbon atom notmore than 6 carbon atoms removed from the carboxyl group.

It has already been taught in US. Pat. 2,940,930 that high droppingpoint greases (500 F. or greater) can be prepared from mixtures ofmonocarboxylic and dicarboxylic acids. However, in preparing the greasesdescribed in that patent, it was necessary to also include a glycol.

The presence of a glycol is undesirable because it renders the greaseprone to oxidation and makes the water resistance of the greaseundesirably low in some applications. The present invention makespossible the preparation of high dropping point greases from hydroxyfatty acids without the necessity of incorporating a glycol.

While U.S. Pats. 3,223,633 and 3,223,624 teach the preparation of highdropping point greases from a 3-component mixture of acids, the presenceof a C to 0., fatty acid salt, which is an esesntial component of thosegreases, is frequently undesirable because of the tendency of suchgreases to undergo surface hardening on standing.

The hydroxy fatty acid employed in preparing the greases of thisinvention will have from about 12 to 24, or more usually about 16 to 20carbon atoms, and will preferably be a hydroxystearic acid, e.g.,9-hydroxy, 10- hydroxy, or l2-hydroxystearic acid, more preferably thelatter. Ricinoleic acid, which is an unsaturated form of12-hydroxystearic acid, having a double bond in the 9- 10 position, canalso be used. Other hydroxy fatty acids include 12-hydroxybehenic acidand IO-hydroxypalmitic acid.

When a second hydroxycarboxylic acid is used along with the boric acidand hydroxy fatty acid, it will be one having an OH group attached to acarbon atom that is not more than 6 carbon atoms removed from thecarboxyl group. This acid has from 3 to 14 carbon atoms and can beeither an aliphatic acid such as lactic acid, -hydroxydecanoic acid,3-hydroxybutanoic acid, l-hydroxycaproic acid, 4 hydroxybutanoic acid,6-hydroxy-alphahydroxystearic acid, etc. or an aromatic acid such asparahydroxybenzoic acid, salicylic acid, 2-hydroxy-4-hexylbenzoic acid,metahydroxybenzoic acid, 2,5-dihydroxybenzoic acid (gentisic acid);2,6-dihydroxybenzoic acid (gamma resorcylic acid);(4-hydroxy-4-methoxybenzoic acid, etc. or a hydroxyaromatic aliphaticacid such as orthohydroxyphenyl, metahydroxyphenyl, or parahydroxyphenylacetic acid. A cycloaliphatic hydroxy acid such as hydroxycyclopentylcarboxylic acid or hydroxynaphthenic acid could also be used.Particularly useful hydroxy acids are lactic acid, salicylic acid, andparah'ydroxybenzoic acid.

In place of the free hydroxy acid of the latter type when preparing thegrease, one can use a lower alcohol ester, e.g., the methyl, ethyl, orpropyl, isopropyl, or sec-butyl ester of the acid, e.g., methylsalicylate, to give a better dispersion when the salt is insoluble. Theamount of lithium salt of the hydroxy acid will range from about 0.1 toabout 10 wt. percent of the finished grease, or preferably from about0.2 to about 5 wt. percent. The monolithium salt or the dilithium saltof the second hydroxy acid can be used, but the dilithium salt ispreferred.

The total soap and salt content of the grease will be in the range offrom about 2 to 30 wt. percent and preferably about 5 to 20 wt. percent.The proportion of the C to C hydroxy fatty acid to boric acid will be inthe range of a weight ratio of about 3 to 100 parts, or more usuallyabout 5 to parts, of hydroxy fatty acid per part by weight of boricacid. There will be a weight ratio of about 0.1 to 10, or more usuallyabout 0.5 to about 5 parts of said second hydroxycarboxylic acid perpart by weight of boric acid in the case of the greases made from 3 acidcomponents.

The lubricating oil base that is used in preparing the greasecompositions of this invention can be any of the conventionally usedmineral oils, synthetic hydrocarbon oils, or synthetic ester oils, andwill generally have a viscosity within the range of about 35 to 200 SUSat 210 F. Synthetic lubrictaing oils that can be used include esters ofdibasic acids such as di-Z-ethylhexyl sebacate, esters of glycols' suchas the C oxo acid diester of tetraethylene glycol, or complex esterssuch as a complex ester formed by reacting l mole of sebacic acid with 2moles of tetraethylene glycol and 2 moles of 2-ethylhexanoic acid. Othersynthetic oils that can be used include synthetic hydrocarclude thepolyphenyl ethers, e.g., those having from about 3 to 7 ether linkagesand about 4 to 8 phenyl groups. (See US. Pat. 3,424,678, column 3.)

The greases can be prepared by coneutralizing all three types of acid,or alternatively by first neutralizing the boric acid and hydroxy fattyacid together and then forming the lithium salt of the secondhydroxycarboxylic acid.

The following examples, which include preferred embodiments, arepresented to illustrate the preparation and various characteristics ofgreases manufactured according to this invention. Comparative examplesare also included to show that inferior results are obtained if boricacid is omitted or if the boric acid is neutralized beyond themonolithium salt stage.

Example 1 (including comparative greases) A grease designated grease Awas prepared using as the thickener system a combination of lithium12-hydroxystearate and monolithium borate. The base oil used inpreparing this grease was a solvent-refined Mid-Continent lubricatingoil distillate known as Solvent 450 Neutral, having a viscosity at 100F. of about 450 SUS. The 12- hydroxystearic acid was added to a portionof the base oil (about /2 of the total oil used in the complete grease)and the mixture was heated to a temperature sufliciently high to meltthe 12-hydroxystearic acid, this temperature being about 180 F. to 190F. Then the boric acid and the lithium hydroxide monohydrate were addedas an aqueous solution, and the resulting mixture was stirred and heatedto a final temperature of about 380 F. to 390 P. Then the remainingportion of the base oil was added and the mixture was cooled to ambienttemperature and milled in a conventional grease mill. A comparativegrease corresponding to A but omitting the boric acid was also prepared.

Two additional greases were prepared using in each case the sameproportion of l2-hydroxystearic acid and boric acid to base oil as ingrease A but increasing the amount of lithium hydroxide monohydrate soas to form dilithium borate and trilithium borate instead of monolithiumborate.

Each of the greases thus prepared was measured for dropping point andfor ASTM penetration at 77. F. The composition of the greases and theinspections are shown in Table I which follows:

Example 2 Two greases were prepared using as the thickener system acombination of dilithium salicylate, lithium 12-hydroxy-stearate andmonolithium borate, the proportions of the thickener components beingvaried as between the two greases. The base oil used in preparing thesegreases was a solvent refined Mid-Continent lubricating oil distillateknown as Solvent 600 Neutral, having a viscosity at F. of about 600 SUS.Methyl salicylate and 12-hydroxystearic acid were added to a portion ofthe base oil and the mixture was heated. After it was observed that the12-hydroxystearic acid had melted, the temperature being then about F.to F., all of the lithium hydroxide that was to be used in forming thevarious lithium salts was added in the form of a 10% aqueous solution towhich had also been aded the boric acid that was to be used in makingthe grease. The resulting mixture was stirred and heated to a finaltemperature of about 380 F. to 390 F. Then the remaining portion of thebase oil was added and the mixture was cooled to about 250 F. at whichpoint an antioxidant and other components of the grease such as rustinhibitors were incorporated. The grease was then milled in aconventional grease mill.

Comparative example Using the same procedure as in Examaple 2,comparative greases were prepared in which one case the methylsalicylate was omitted, in a second case the boric acid was omitted andin the third case both the boric acid and methyl salicylate wereomitted. In each instance the corresponding quantity of lithiumhydroxide needed to form the soap or salt of the omitted component wasalso omitted.

Each of the greases prepared as in Example 2 and in comparative examplewas measured for dropping point and for ASTM penetration at 77 F. Thecomposition of each of the greases and the inspections are shown inTable II which follows.

TABLE II Greases of invention Comparative greases M N X Y Z Composition,weight percent:

IAOH'HZO 4. 0 1. 9 2. 5 2. 9 1. 8 12-hydroxystearic acid 12. 9 10. 4 12.9 11. 5 12. 9 Boric acid 1. 1 0. 5 1. 1 Methyl salicylate 2. 7 0. 5 2. 5Base oil 78. 3 84. 7 82. 5 81. 1 85. 3 Phenyl alpha naphthyline 1.0 1.01 0 1.0 Na-Sul-B SN 1. 0 1. 0 Inspections:

Dropping point, F 500+ 500+ 437 415 405 ASTM penetration at 77Unworked--. 252 275 262 217 261 60 strokes... 201 280 255 240 250 10,000strokes 293 299 291 242 277 The phenyl alpha naphthylamine referred towas used as an antioxidant. The Na-Sul-BSN is a trademarked productwhich serves as a rust inhibitor; it is a 50 wt. percent concentrate, ina light mineral oil, of a neutral bar-' ium salt of dinonyl naphthalenesulfonic acid derived from naphthalene alkylated with tripropylene.

Referring to the data in Table II, comparison of grease X with grease Zand with grease M shows that while incorporation of monolithium borateinto a lithium hydroxystearate grease increases the dropping pointsomewhat, much greater increase in dropping point results when lithiumsaiicylate is also used. Comparison of greases Y and Z shows thatincorporation of the lithium salicylate without the monolithium boratedoes not improve the dropping point significantly.

Various other conventional additives can be incorporated into the greasecompositions of this invention, as is understood by those skilled in theart. Such additives include antioxidants, rust inhibitors, tackinessagents, odor modifiers, dyes, extreme pressure agents, etc.

It wilrl be understood that the specific examples herein presented areby way of illustration and not limitation. The scope of this inventionis to be determined by the appended claims.

What is claimed is:

1. A lubricating grease composition of high dropping point whichcomprises a major proportion of a lubricating oil and from about 2 to 30wt. percent of a thickener system whose essential components include alithium soap of a C to C hydroxy fatty acid and a monolithium salt ofboric acid, wherein there are from 3 to 100 parts by weight of hydroxyfatty acid per part by weight of boHc acid.

2. Composition as defined by claim 1 wherein the thickener system alsoincludes as a third component a lithium salt of a secondhydroxycarboxylic acid of from 3 to 14 carbon atoms, wherein the hydroxygroup is attached to a carbon atom not more than 6 carbon atoms removedfrom the carboxy group, and wherein there is a weight ratio of fromabout 0.1 to about 10 parts of said second hydroxycarboxylic acid perpart of boric acid.

3. Grease composition as defined by claim 1 wherein said hydroxy fattyacid is 12-hydroxystearic acid.

4. Grease composition as defined by claim 2 wherein said secondhydroxycarboxylic acid is salicylic acid.

5. Grease composition as defined by claim 2 wherein said secondhydrocarboxylic acid is lactic acid.

6. Grease composition as defined by claim 2 wherein said secondhydroxycarboxylic acid is parahydroxybenzoic acid.

References Cited UNITED STATES PATENTS 2,614,076 10/ 1952 Moore et al252-42.1

2,951,808 9/1960 Norton et al. 25218 2,987,476 6/ 1961 Hartley et a125218 FOREIGN PATENTS 778,468 7/1957 Great Britain 25218 PATRICK P.GARVIN, Primary Examiner A. H. METZ, Assistant Examiner US. Cl. X.R.2s2-25, 42.1

